Many electronic devices are powered by batteries. Rechargeable batteries are often used to avoid the cost of replacing conventional dry-cell batteries and to conserve precious resources. However, recharging batteries with conventional rechargeable battery chargers requires access to an alternating current (AC) power outlet, which is sometimes not available or not convenient. It would, therefore, be desirable to derive power for electronics wirelessly.
Magnetic or induction based coupling requires a charger and the receiver to be in relatively close proximity to one another. Wireless charging of devices across a larger distance, however, requires more advanced mechanisms, such as transmission via radio frequency (RF) signals, ultrasonic transmissions, laser powering, etc., each of which present a number of unique hurdles to commercial success.
Regardless of the transmission medium, any time energy is transferred through a free space, such as within a residence, commercial building, or other habited environments, it is desirable to limit the exposure levels of the transmitted signals. Power delivery is constrained to relatively low power levels (typically on the order of milliwatts). Due to this low energy transfer rate, it is imperative that a wireless power transmission system be as efficient as possible.
Accordingly, a need exists for technology that overcomes the problem demonstrated above, as well as one that provides additional benefits. The examples provided herein of some prior or related systems and their associated limitations are intended to be illustrative and not exclusive. Other limitations of existing or prior systems will become apparent to those of skill in the art upon reading the following Detailed Description.